When putting a golf ball, the most accurate and consistent results are achieved when the stroke of putter club head coincides with an intended line of travel of the golf ball, and the frontal surface of the club head is maintained perpendicular to the intended line of travel. This is because the point of impact between the putter and the golf ball determines the actual line of travel of the golf ball, neglecting variations in putting green slope.
Most experienced golfers are able to keep the stroke more or less in coincidence with the intended line of travel, but many have difficulty maintaining the club head perpendicular to the line of travel. A club head that is horizontally inclined toward the golfer on impact with the golf ball is said to be "closed", while a club head that is horizontally inclined away from the golfer on impact with the golf ball is said to be "opened". When the frontal surface of a putter club head is flat (as is usually the case), closing the club head moves the point of impact away from the golfer, while opening the club head moves the point of impact toward the golfer. Thus, closing the club head causes the ball to go left of the intended line of travel, while opening the club head causes the ball to go right of the intended line of travel. In the case of a 10-foot putt, for example, opening or closing the club head by only 3.0 degrees causes the ball to miss the center of the hole by 6.3 inches.
Others have recognized the above-described problem, and various club head configurations have been proposed to compensate for stroke variations. See, for example, the U.S. Pat. Nos. 3,989,257 to Barr; 4,121,833 to Prueter; and 5,213,332 to Fahy et al. These patents each propose the use of a curved club head that tends to mitigate the effect of opening and closing.
Another problem experienced by golfer occurs due to variations in the vertical angle of the club head when the putter strikes the golf ball. This may be due to variations in the position of the golfer's hands or feet relative to the ball. The frontal surface of a putter club head is customarily angled with respect to the vertical to impart a certain amount of loft to the golf ball, but the degree of loft actually achieved changes with the above-described variations, making it difficult for the golfer to putt consistently.
Accordingly, what is needed is a putter that compensates for a variety of stroke anomalies, enabling the golfer to putt more accurately and consistently in spite of the anomalies.